JPH0449164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applied to a video tape recorder (hereinafter referred to as VTR).
The rotary head assembly is referred to as a rotary head assembly.

Conventional Structure and Problems As shown in FIG. 1, the rotary head assembly of a VTR consists of an upper cylinder 1 and a lower fixed cylinder 2, which have approximately the same outer diameter and are coaxially arranged.
In the gap between the upper cylinder 1 and the lower fixed cylinder 2, a magnetic head 3 whose tip protrudes outward from the cylindrical surface of the two cylinders and rotates coaxially with the two cylinders is constructed. In addition, in the case of a system in which the upper cylinder 1 rotates, the magnetic head 3 is attached near the outer periphery of the lower end surface of the upper cylinder 1.
In the case of a fixed type, it is attached to the outer periphery of a rotating member (not shown) that rotates about the same axis between the two cylinders. The magnetic tape 4 is
It is wound helically around this rotating head assembly and runs at a constant speed. Reference numeral 5 denotes a stepped portion (hereinafter referred to as a lead) for regulating the running position of the magnetic tape 4 in the width direction. The magnetic tape 3 rotates at 1800 rpm per minute, and video signals are recorded and reproduced on the magnetic tape 4.

FIGS. 2 and 3 are cross-sectional views of two conventional configurations of the rotary head assembly. In Fig. 2, 5 is the rotation axis;
It is rotatably supported by bearings 6 and 7, and rotationally driven by a drive motor (not shown). The magnetic head 8 is fixed to the rotating shaft 5 via a rotating member 9 and rotates at a predetermined speed. Upper fixed cylinder 10
is coaxially connected to the lower fixed cylinder 12 via the member 11, and further connected to the lower fixed cylinder 12.
is fixed on the base of the VTR. 13,
14 is a collar, and 15 is a bearing retaining ring. While the upper cylinder is fixed in Figure 2, the 3rd cylinder is fixed.
The figure shows the configuration of the upper cylinder rotation system. In FIG. 3, 16 is an upper rotating cylinder, and 17 is a rotating shaft, which are rotatably supported coaxially with a lower fixed cylinder 19 via a bearing 18, and are rotated by a drive motor (not shown). Driven. 2
A magnetic head 0 is attached to the outer periphery of the lower end surface of the upper rotating cylinder 16 so as to protrude from the cylindrical surface formed by both the upper and lower cylinders in the gap between the upper rotating cylinder 16 and the lower fixed cylinder 19.

Now, when the magnetic tape runs on the rotating head assembly as described above, its magnetic surface makes sliding contact with the rotating head assembly. At this time, the contact pressure between the magnetic head and the upper and lower cylinder surfaces is determined by the tape tension, and is on average 3 to 60 gf/
^cm2 . Further, the magnetic tape running speed is on the order of 1 to 10 cm/sec in recording/reproducing mode.

FIG. 4 schematically shows the sliding contact state of the magnetic tape on the conventional rotary head assembly. In FIG. 4, 21 is the upper cylinder;
22 is a lower fixed cylinder, and 23 is a magnetic tape. Since the magnetic tape is highly deformable, the contact state is not uniform on the outer peripheral surfaces of the upper and lower cylinders, and as shown in FIG. 4, the contact state varies greatly depending on the location. In other words, the edge 24 at the lower end of the upper cylinder 21 and the edge 25 at the upper end of the lower fixed cylinder 22 have a locally severe contact state as shown in FIG. Furthermore, since the magnetic tape runs helically wrapped around the rotating head assembly, the longitudinal position of the magnetic tape,
In other words, the state of contact between the magnetic tape and the cylinder varies greatly depending on the circumferential position on the rotary head assembly. In particular, at the tape exit side of the cylinder, the tape tension increases due to frictional force, so the contact pressure between the magnetic tape and the upper and lower cylinders increases. Further, the magnetic head for recording and reproducing video signals slides into contact with the magnetic tape at a high speed of about 6 m/sec under a predetermined contact pressure.

Now, as mentioned above, the magnetic tape runs on the rotating head assembly under complicated mechanical conditions, and the problems therein can be summarized as follows.

(1) Tape squealing phenomenon due to sliding contact between the upper and lower cylinders; When the magnetic tape contacts and slides against the upper and lower cylinders, a type of self-excited frictional vibration may occur. The conditions under which this vibration occurs is greatly influenced by the tape tension, the surface properties of the tape and cylinder, or the surrounding humidity. The basic form of vibration is longitudinal vibration of the tape, which causes color unevenness and jitter in recorded and reproduced images on a VTR, and in extreme cases, produces sharp sounds (several hundred to several thousand Hz).

(2) Adhesion phenomenon of the magnetic tape to the upper and lower cylinders; Generally, the surface roughness of the magnetic tape is on the order of several hundred Å and is extremely smooth. In addition, to avoid tape damage on the cylinder surface,
Consists of a smooth surface (surface roughness 0.1S to 1S). When two extremely smooth surfaces are brought into contact in this way, they generally stick together. In VTR tape running systems, this phenomenon occurs when the magnetic tape sticks to the outer circumferential surfaces of the rotating head assembly, especially the upper and lower cylinders, and the magnetic tape may become unable to run, which occurs in a humid atmosphere. Easy to do.

(3) Tape damage and wear occur due to friction between each part of the rotating head assembly and the magnetic tape; as mentioned above, the magnetic tape and rotating head assembly are subject to surface pressures of 3 to 60 gf/cm ² on average. Because of the contact and sliding movement, the tape running surface of the rotary head assembly is subject to wear, while the magnetic tape surface is also subject to wear and peeling of the magnetic material.
In particular, wear and tear on the magnetic tape, or tape damage, not only causes loss of magnetic recording signals, but also causes damage to the magnetic tape.
The fallen magnetic powder accelerates wear at various sliding parts, and furthermore, accumulates in the head gap of the magnetic head and causes clogging, making recording and reproduction impossible.

Especially this cylinder wear and tape damage.
Exhibits harsher sliding conditions. This is noticeable at the edges of the lower end of the upper cylinder and the upper end of the lower fixed cylinder.

The fundamental cause of all of these problems is that the magnetic tape contacts and slides against the rotating head assembly.

On the other hand, with the trend toward smaller and lighter VTRs,
In order to improve the signal recording density on magnetic tape, we are moving away from conventional tapes coated with magnetic powder of iron oxide or chromium dioxide along with a resin binder, to use so-called alloy tapes or vapor-deposited tapes as magnetic tapes. It is in. While the magnetic surface of conventional tapes is made of resin and magnetic powder, the magnetic surface of these new tapes is just a metal surface, so the coefficient of friction when sliding against stainless steel, for example, is low. , will rise from the previous level of around 0.2 to around 0.5. Therefore, the above-mentioned problems associated with sliding in a rotating head assembly in which the magnetic surfaces are in sliding contact are brought into greater focus than with conventional tapes.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks and provides a rotary head assembly that enables high-quality image recording and reproduction with high reliability.

Structure of the Invention The present invention is divided into a case where the upper cylinder is fixed and a case where the upper cylinder is rotated. , a rotating member having a magnetic head protruding outwardly from the outer circumferential surface of the fixed cylinder in the gap and mounting a magnetic head that rotates about the same axis as the fixed cylinder, the end face of the fixed cylinder facing the end face of the rotating member; Among them, a pump-out type spiral groove that has an air blowing effect is provided in the area where the magnetic tape is enclosed,
The structure is such that a pump-in type spiral groove having an air suction effect is provided in an area where the magnetic tape is not included. In the latter case, the lower fixed cylinder has approximately the same diameter as the lower fixed cylinder and is arranged coaxially in the gap, and in the gap, the lower fixed cylinder protrudes outward from the outer peripheral surface of the lower fixed cylinder. It has an upper rotating cylinder on which a magnetic head that rotates around the same axis as the fixed cylinder is mounted, and a pump-out type is installed on the end surface of the lower fixed cylinder that faces the end surface of the rotating cylinder, in the area where the magnetic tape is enclosed. A pump-in type spiral groove is provided in an area where the magnetic tape is not included, and air blown out from the spiral groove is used to create an air film between the rotating cylinder and the magnetic tape. It has the unique effect of reducing tape squeal and tape damage caused by sliding friction of the magnetic tape, as well as reducing wear of the rotating cylinder.

DESCRIPTION OF EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 5 shows a cross-sectional view of a rotary head assembly in a first embodiment of the present invention. Fig. 5 shows the structure of the upper cylinder fixing system, in which 26 is a rotating shaft and bearing 2
7, and is rotationally driven by a drive motor (not shown). A magnetic head 28 is fixed to a rotating shaft 30 via a rotating member 29, and rotates at a predetermined speed. Upper fixed cylinder 3
0 is connected to the lower fixed cylinder 3 via the support member 31
2, and a lower fixed cylinder 32 is fixed on the base of the VTR.
33 is a spiral groove formed on the end surface of the lower fixed cylinder 32 facing the rotating member 29;
is a spiral groove formed on the end surface of the upper fixed cylinder 30. The end faces of the rotating member 29 and the lower fixed cylinder 32 and the rotating member 29 and the upper fixed cylinder 30 are set so that the gap δ ₁ is a constant value. 35 is a collar, and 36 is a bearing retaining ring.

FIG. 6 shows a top view of the lower fixed cylinder 32 in the above embodiment, and shows the pattern of the spiral grooves 33. 31 is a support member, 37 is a magnetic tape, 38, 39
is a guide post that regulates the winding angle of the magnetic tape 37. Further, a indicates the rotation direction of the rotating member 29. The spiral groove is provided on a ring-shaped end face surrounded by two concentric circles with radii r ₁ and r ₂ , and the blacked-out portion 40 in the figure is the groove, and 41 is the land portion. As shown in FIG. 6, the setting angle ρ of the spiral groove is a pump-out type spiral groove in the area facing the magnetic tape 37, and a pump-in type spiral groove in the area not facing the magnetic tape 37.

To show the specific setting values of the spiral groove in this example, in Fig. 6, r ₁ = 38 mm,
r ₂ =40 mm, and a spiral groove is provided on a ring-shaped surface with a width of 2 mm. Further, the set angle β is 15°. Groove 40 and land 41 are at an angle
They are arranged at equal pitches of 7.5°, and their cross-sectional shape is as shown in Figure 7. In FIG. 7, δ ₁ is 30 μm and h ₁ is 120 μm.

Regarding the spiral groove 34 provided in the upper fixed cylinder 30, a pump-out type spiral groove is provided on the end face facing the magnetic tape, and a pump-in type spiral groove is provided on the other end faces.Detailed dimensions are as described above. Same as setting value.

The operation of the rotary head assembly constructed as above will be explained below. In FIG. 6, when the rotating member 29 rotates in the direction indicated by arrow a, the pump-in type spiral groove provided in the area not facing the magnetic tape 37 passes through the gap δ ₁ with the rotating member 29 to the cylinder. Outside air is drawn into the cylinder. On the other hand, air inside the cylinder is blown out of the cylinder from a pump-out type spiral groove provided in an area facing the magnetic tape 37 through a gap δ ₁ with the rotating member 29. That is, air outside the cylinder is sucked into the cylinder interior space and is blown out to the outside of the cylinder again. The air flow near the cylinder is shown in Figure 6b.
Indicated by c. Now, considering the air pressure in the cylinder internal space, the magnetic tape 37 acts to prevent the air in the cylinder internal space from being blown out to the outside, so the pump-in type and pump-out type spiral grooves have approximately the same length ( In the case of this embodiment in which the magnetic tape of the VTR has a winding angle of 190° to 220°, the amount of air taken into the cylinder is greater than the amount of air blown out. Therefore, the air pressure in the cylinder internal space becomes higher than the external air pressure, and the amount of air blown out from the cylinder internal space can be set to be larger than when only a pump-out type spiral groove is provided.

As described above, by setting the amount of air intake by the pump-in type spiral groove to be greater than the amount of air blown out by the pump-out type spiral groove, and aiming to increase the amount of air blown out,
A floating force is applied to the magnetic tape 37, and a uniform air film can be formed on the circumferential wall surfaces of the upper fixed cylinder 30 and the lower fixed cylinder 32 over the entire area on which the magnetic tape 37 slides. Therefore, sliding contact between the magnetic tape 37 and the rotary head assembly can be avoided, and stable and smooth tape running can be realized.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 8 shows a cross-sectional view of a rotary head assembly in a second embodiment of the invention. 8th
The figure shows the configuration of the upper cylinder rotation method.
2 is an upper rotating cylinder, 43 is a lower fixed cylinder, and 44 is a lead portion that guides the running position of the magnetic tape in the width direction. 45 is a shaft;
An upper rotating cylinder is fixed via a disk 46. Further, 47 and 48 are ball bearings that rotatably support the shaft 45, 49 is a collar that applies preload to the ball bearing and fixes it, and 50 is a spacer. Reference numeral 51 denotes a spiral groove provided on the end surface of the lower fixed cylinder 43 facing the upper rotating cylinder 42. The end faces of the upper rotating cylinder and the lower fixed cylinder are set so that the gap δ ₁ is a constant value.

FIG. 9 shows a top view of the lower fixed cylinder 43 in the above embodiment, and shows the pattern of the spiral grooves 51. 52 is a magnetic tape, and 53 and 54 are guide posts. The spiral groove is provided on a ring-shaped surface surrounded by two concentric circles with radii r ₁ and r ₂ , and the blacked-out portion 55 in the figure is the groove and 56 is the land. In FIG. 9, the setting angle β of the spiral groove is between the magnetic tape 52 and the lower fixed cylinder 43.
The values are different between areas where the circumferential surfaces of the grooves face each other and areas where they do not face each other, and the opposing areas have pump-out type spiral grooves, while the areas where they do not face each other have pump-in type spiral grooves. Moreover, the specific setting values of the spiral groove in this embodiment are the same as those in the first embodiment, and are r ₁ =38 mm, r ₂ =40 mm, β=15°. Further, the grooves 55 and lands 56 are provided at equal pitch intervals of 7.5 degrees, and their cross-sectional shape is the same as that shown in FIG. 7 for the first embodiment.

The operation of the rotary head assembly constructed as above will be explained below.

When the upper rotating cylinder 42 rotates at high speed (1800 rpm in the VHS system) in the direction shown by arrow a, the air is transmitted through the gap δ ₁ between the spiral groove provided in the area not facing the magnetic tape 52 and the upper rotating cylinder 42. , air outside the cylinder is sucked into the cylinder. On the other hand, through the gap δ ₁ between the spiral groove provided in the area facing the magnetic tape 52 and the upper rotating cylinder 42,
Air inside the cylinder is blown out to the outside of the cylinder. That is, the air outside the cylinder is sucked into the space inside the cylinder and is blown out to the outside of the cylinder again. The air flow near the cylinder is shown by d and e in Fig. 9. Now, considering the air pressure in the cylinder interior space, the magnetic tape 52 prevents the air in the cylinder interior space from being blown out to the outside, so the lengths of the pump-in type and pump-out type spiral grooves are approximately equal in this embodiment. (The magnetic tape wrapping angle of a VTR is 190°), the amount of air taken into the cylinder is greater than the amount of air blown out. Therefore, an air film is formed between the magnetic tape 52 and the rotating cylinder assembly, thereby avoiding sliding contact and preventing tape squeal or tape sticking. This results in
It is possible to record and reproduce high quality images with high reliability.

Effects of the Invention As described above, the present invention provides a pump-out type for the area where the magnetic tape is included on the end face of the fixed cylinder facing the end face of the rotating body on which the magnetic head is mounted, and the area where the magnetic tape is not included. The rotating head assembly is configured with a pump-in spiral groove to form a stable air film layer between the magnetic tape and the rotating cylinder, thereby reducing the amount of friction caused by sliding between the magnetic tape and the rotating head assembly. This technology reduces tape squeal, tape damage, etc., and makes it possible to record and reproduce high-quality images with high reliability, which has great practical effects.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the rotating head assembly; Figure 2 is a perspective view of the rotary head assembly;
3 is a front sectional view of a conventional rotary head assembly, FIG. 4 is a partially enlarged sectional view of a conventional rotary head assembly schematically showing a tape running state, and FIG. 5 is a front sectional view of a conventional rotary head assembly. FIG. 6 is a front sectional view of the rotary head assembly in the first embodiment; FIG. 6 is a top view of the lower fixed cylinder in the first embodiment;
8 is a front sectional view of the rotary head assembly in the second embodiment, and FIG. 9 is a top view of the lower fixed cylinder in the second embodiment. 28... Magnetic head, 29... Rotating member, 30
...Upper fixed cylinder, 32...Lower fixed cylinder, 33, 34...Spiral groove.

Claims (1)

[Scope of Claims] 1. A pair of fixed cylinders having substantially the same diameter and arranged coaxially with a gap between them, and a pair of fixed cylinders that are rotatably provided in the gap and protrude outward from the outer peripheral surface of the fixed cylinder. and a rotating member equipped with a magnetic head that rotates about the same axis as the fixed cylinder, the end face of the fixed cylinder facing the end face of the rotating member having an air blowing effect on a region enclosed by the magnetic tape. 1. A rotary head assembly comprising: a spiral groove having an air suction action in an area where the magnetic tape is not enclosed; 2. A fixed lower fixed cylinder, which has approximately the same diameter as this lower fixed cylinder, is arranged coaxially with a gap, and protrudes outward from the outer peripheral surface of the lower fixed cylinder into the gap, and has the lower fixed cylinder. It consists of an upper rotating cylinder equipped with a magnetic head that rotates around the same axis as the cylinder, and has an air blowing effect on the area where the magnetic tape is enclosed on the end face of the lower fixed cylinder that faces the end face of the upper rotating cylinder. Provided with a spiral groove,
A rotary head assembly including a spiral groove having an air suction effect in an area where the magnetic tape is not included.